This invention relates to band saw machines of the commerical type in which an endless saw blade band is looped about a pair of wheels, one of which is driven. The wheels are usually mounted in the saw head or housing, and in some of these machines the housing is hinged, while in other types it is mounted on vertical posts or guides. In some installations the blade is moved through the work, while in other types of machines the work is fed through the blade. Approximately midway between the wheels of all band saws, a pair of saw guides are located, which are spaced apart a distance greater than the cross-sectional size of work pieces to be cut by the machines. These saw guides hold the blade at a fixed angle, apply uniform pressure to the back edge of the band saw blade and define the cutting span of the blade. As the teeth of the blade cut through the work piece, all teeth in contact with the work have an equal, albeit, minimum force applied thereto. This causes the blade to bow outwardly from the kerf of the work and each tooth does not cut as full a chip as it is inherently capable of cutting. When cutting very hard or large work pieces, the cutting efficiency of conventional band saws is thus relatively low and this is manifested by relatively long cutting times and short blade life per unit cross-sectional diameter of the work piece.
A number of solutions have been suggested in the prior art to overcome these drawbacks. In many of these prior art approaches, the configuration of the band saw blade itself has been modified. One such proposal is disclosed in my prior U.S. Pat. No. 4,423,653 granted on Jan. 3, 1984, which refers to a number of earlier patents including U.S. Pat. Nos. 4,195,543; 4,160,397; 4,205,571; 1,850,478; 817,361; 286,706; and Canadian Pat. No. 883,602. In U.S. Pat. No. 4,205,571, dated June 3, 1980 to Bertini, a band saw blade is disclosed in which the rear edge of the blade is progressively tapered or inclined relative to the cutting edge and the minimum and maximum transverse sections of the blade are contiguous to define a sharp drop-off or cam-step between the gradually tapered back edge portions of the blade. The purpose of this construction is to effect a progressive or gradual change in the cutting angle of the blade relative to a work piece, first in one direction and then in the opposite direction. This type of gradual or progressive change in the cutting angle of the blade is also disclosed in Bertini U.S. Pat. Nos. 4,160,397 and 4,023,448. German Patent Application No. DE 27-48-822, dated Mar. 5, 1978, also shows a band saw having progressively tapered sections with a cam-step portion between the tapered sections.
In my U.S. Pat. No. 4,423,653, an improved band saw blade construction is disclosed in which the blade alternately cuts at two different angles relative to the work place. The blade dwells or remains at its extreme cutting angles for approximately seventy (70%) percent of the duration of each cycle. Thus the blade remains at each of its maximum angles of tilt for about thrity-five (35%) percent of each cycle of oscillation and is rapidly tilted to the opposite angle of tilt and again held fixed for approximately thirty-five (35%) percent of the cycle. Using this type of blade construction, the work is cut for a major percentage of cycle time at a fixed angle relative to the work which is in direct contrast to a saw blade having a progressively sloped or tapered back edge, such as disclosed in Bertini U.S. Pat. No. 4,160,397. Significantly, blades constructed in accordance with my U.S. Pat. No. 4,423,653, achieve a thrity (30%) percent improvement in cutting speed over blades of the type disclosed in the Bertini patent.
In Japanese Patent Applications Nos. 57-107729 and 57-163020, each disclose a band saw machine in which the saw is uniformly oscillated and at its extreme angles of tilt, the weight of the saw frame is allowed to drop or fall to achieve uniform cutting depth.
Blucher U.S. Pat. No. 4,127,045 discloses a step-cam mechanism which moves the band saw gradually toward the work and then instantaneously releases the band at the radial step of the cam 92. The step-cam thus provides an equivalent cutting action to the saw blade disclosed in Bertini U.S. Pat. No. 4,205,571, wherein the blade is gradually tilted to an ever increasing angle and then instantaeously released. As disclosed in the Blucher Patent, an improvement in cutting speed of about five (5%) percent is achieved, while in Applicant's concept of aternately varying the cutting angle between two extreme angles results in an improvement in cutting time of approximately fifty (50%) percent over a conventional blade.
The principal object of this invention is to provide an improved method of oscillating a band saw blade in a manner to achieve greatly improved cutting speeds and improved blade wear.
Another object of this invention is to provide an oscillating band saw machine in which the cutting angle of the band saw blade is alternately varied from one extreme cutting angle relative to the work to the opposite extreme cutting angle, whereby greatly improved cutting speeds and improved blade wear result.
A further object of this invention is to provide a machine which duplicates the oscillatory cutting action and performance achieved by the saw blade construction of my U.S. Pat. No. 4,423,653.